<template>
  <scroll @scroll="scroll"
          :listen-scroll="listenScroll"
          :probe-type="probeType"
          :dataA="dataA"
          class="listview"
          ref="listview">
		<!-- 左侧歌手列表 -->
    <ul>
      <li v-for="(group,index) in dataA" :key="index" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <uL>
          <li @click="selectItem(item)" v-for="(item, index) in group.items"  :key="index" class="list-group-item">
            <img class="avatar" v-lazy="item.avatar">
            <span class="name">{{item.name}}</span>
          </li>
        </uL>
      </li>
    </ul>
		<!-- 右测字母列表 -->
    <div class="list-shortcut" 
				 @touchstart.stop.prevent="onShortcutTouchStart" 
				 @touchmove.stop.prevent="onShortcutTouchMove"
         @touchend.stop>
      <ul>
        <li v-for="(item, index) in shortcutList" :data-index="index"  :key="index" class="item"
            :class="{'current':currentIndex===index}">{{item}}
        </li>
      </ul>
    </div>
		<!-- tip文字 -->
    <div class="list-fixed" ref="fixed" v-show="fixedTitle">
      <div class="fixed-title">{{fixedTitle}} </div>
    </div>
    <div v-show="!dataA.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
  import Scroll from 'base/scroll/scroll'
  import Loading from 'base/loading/loading'
  import {getData} from 'common/js/dom' //自定义dom结构

  const TITLE_HEIGHT = 30 //title 的高度
  const ANCHOR_HEIGHT = 18//字母表的高度

  export default {
    props: {
      dataA: {
        type: Array,
        default:[]
      }
    },
    computed: {
      shortcutList() {//循环得到字母的首字母
        return this.dataA.map((group) => {
          return group.title.substr(0, 1)
        })
      },
      fixedTitle() { //字母列表的title头 边界问题
        if (this.scrollY > 0) {
          return ''
        }
        return this.dataA[this.currentIndex] ? this.dataA[this.currentIndex].title : ''
      }
    },
    data() {
      return {
        scrollY: -1, //监听时时滚动的位置
        currentIndex: 0,
        diff: -1//热门字母表的title
      }
    },
    created() {
      this.probeType = 3
      this.listenScroll = true
      this.touch = {}
      this.listHeight = []
    },
    methods: {
      selectItem(item) {
        this.$emit('select', item)
      },
      onShortcutTouchStart(e) { //手指接触
				let anchorIndex = getData(e.target, 'index') //获取下标
				// console.log( this.$refs.listviwe.scrollToElement( this.$refs.listviwe.listGroup[anchorIndex],0 ) ) //最初写法
        let firstTouch = e.touches[0] //获取第一个手指的位子
        this.touch.y1 = firstTouch.pageY
        this.touch.anchorIndex = anchorIndex//记录当前的点击的索引
        this._scrollTo(anchorIndex)
      },
      onShortcutTouchMove(e) { //手指移动
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY//相减可以得到滚动的高度 
        let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
        let anchorIndex = parseInt(this.touch.anchorIndex) + delta//等到要滚动几个索引值
        this._scrollTo(anchorIndex)
      },
      refresh() {
        this.$refs.listview.refresh()
      },
      scroll(pos) {//从scroll派发出来的scroll的位置
        this.scrollY = pos.y
      },
      _calculateHeight() { //获取歌手列表的高度值
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for (let i = 0; i < list.length; i++) {
          let item = list[i]
          height += item.clientHeight
          this.listHeight.push(height)	
        }
	      // (24)[0, 760, 1030, 1370, 1780, 1910, 2110, 2450, 2720, 3060, 3190, 3950, 4430, 4700, 4900, 5100, 5370, 5570, 5980, 6460, 7010, 7560, 7900, 9010
      },
      _scrollTo(index) { //封装了要滚动的条数位置
        if (!index && index !== 0) { //首尾2端点击无效
          return
        }
        if (index < 0) { //超出边界
          index = 0 
        } else if (index > this.listHeight.length - 2) {
          index = this.listHeight.length - 2
        }
				//点击字母表是滑动条位子不变 需要手动设置 watch
        this.scrollY = -this.listHeight[index]//手动设置滚动条位置
        this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
      }
    },
    watch: {
      dataA() {
        setTimeout(() => { //延时计算高度 确保每个手机的数据都能兼容
          this._calculateHeight()
        }, 20)
      },
      scrollY(newY) { //比较数组的位置
        const listHeight = this.listHeight
        // 当滚动到顶部，newY>0
        if (newY > 0) {
          this.currentIndex = 0
          return
        }
        // 在中间部分滚动
        for (let i = 0; i < listHeight.length - 1; i++) {
          let height1 = listHeight[i]
          let height2 = listHeight[i + 1]
          if (-newY >= height1 && -newY < height2) {
            this.currentIndex = i
            this.diff = height2 + newY //热门字母表的title
            return
          }
        }
        // 当滚动到底部，且-newY大于最后一个元素的上限
        this.currentIndex = listHeight.length - 2
      },
      diff(newVal) {//热门字母表的title
        let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
        if (this.fixedTop === fixedTop) {
          return
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }
    },
    components: {
      Scroll,
      Loading
    }
  }

</script>


<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>

    
   
 	